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Shrub Diseases

Herbi-Systems has a tree and shrub system dedicated to making your landscape a healthy addition to your lawn. When a fungus or insect attacks your landscape, it could mean costly replacement. Our treatments help to prevent damage and protect your valuable investment. Our trained and licensed staff will regularly inspect and treat your ornamentals with top-quality chemicals. If chemicals are to be used, a certified Herbi-Systems specialist will identify the target disease and apply the correct product at the right rate.

General Problems in Your Landscape

We have listed the most common concerns (where no fungus or disease is present) first then alphabetically.

For information about diseases and fungi, see below.

Establishing Plants

Problems may occur for a number of reasons. Usually, the site is unsuitable for the type of plant, or maintenance after planting is faulty. Soil-borne plant diseases, such as root rots, wilt diseases, or nematode infestations can cause problems even if the site previously supported plants of the same kind. The transplants are more vulnerable to the effects of the disease. Sometimes plants produce toxins that leach into surrounding soil and discourage growth of other plants that might be competing with them. Walnut trees are well known for this. In these cases, one may have to wait a year or more after the removal of the toxin producer to plant replacements.

Mulch Volcanoes

Mulch is good for your trees and shrubs, but you can carry a good thing too far. A common problem is creating a Mulch Volcano, or piling too much mulch near the trunk. Unfortunately, many people think mulch volcanoes look pretty, but too much mulch near the trunk can actually damage your tree. Deep mulch against the trunk can suffocate the roots, compact the soil, and block the penetration of nutrients into the soil. In addition, it can cause cankers (open wounds) on the lower trunk. Once your tree develops cankers, the situation cannot be reversed, and your tree will die within a few seasons. Resist the temptation to make a “mulch volcano.” Leave that donut around the tree trunk.

Tree Decline

Tree decline is a progressive deterioration in the health of a tree that is attributed to a combination of factors, such as competition among plants, environmental stresses, injuries and diseases like defoliating leaf diseases, root rots, wilt diseases, and nematode infestations in the soil. Although each of these may be unimportant individually, in combination they may cause decline and death of the plant. Avoid unnecessary injury. To avoid stress, know and supply the maintenance needs of the plant. Water deeply during dry periods. Don’t induce rapid top growth by applying high nitrogen fertilizers in the root zone. Prevent serious, recurrent defoliating disease with fungicide treatments and treat serious insect and mite infestations.

Annual Needle Shed

Older needles inside shrub yellow. Younger needles remain green. May occur in late spring or early summer, or more slowly over the entire season. A normal part of the growth cycle. No control is necessary.

Fall Needle Shed

Inner branchlets turn yellow, then brown. Outer foliage remains healthy. Normal part of growth cycle. No control is necessary.

Iron chlorosis

Iron Chlorosis

Interveinal chlorosis of youngest leaves. Leaves may eventually become yellow, cream colored, or white. Usually caused by reduced availability of iron in high pH soil. Correct site-related conditions such as high soil pH, water logging, and poor aeration. Iron chelate applied to foliage may provide temporary greening, but for long term control, lower the soil pH.

Leaf Scorch

Leaf Scorch is a symptom that can occur any time the leaves need more water than they receive. It may be caused by diseases of the roots, crown and vascular system; cankers; inadequate available water; high air temperatures; damage to the roots from transplanting, “wet feet,” soil compaction or excavation or natural gas leaks; chemical injury such as herbicides, excessive fertilizer and road salt; root girdling; “pot boundness” that occurred in containers before planting or following planting if roots fail to extend beyond the planting hole. Be sure soil is moist in the fall. Provide windbreaks around plants. Plant adapted varieties in sheltered locations or erect wind barriers.

Spine Spot

Small, grayish-brown to dark punctures and scratches on both leaf surfaces in early spring. Spots caused by wounding of leaves by spines of nearby leaves during windy conditions. Plant in sheltered locations or erect wind barriers.

Wet Feet

Plants turn yellow and brown. Whole plant may die rather rapidly. Usually occurs in spots where moisture has been excessive. Can be complicated by root and crown diseases. Can occur in long established plantings if periods of drought alternate with periods of saturated soils. Maintain good drainage. Plant yews in spots that do not get overly wet.

Winter Injury

Foliage brown and scorched. Twigs die back. Bark splitting. No control is necessary. Protect plant from injury as in frost situations.

Disease or Fungus in Your Landscape

Most diseases or fungi present in your landscape need professional attention. Please contact our office for a free Tree & Shrub Analysis and Estimate.

Black spot

Black Spot

General and serious. Leaves have black spots with irregular margins. Leaflets yellow and drop off. Collect and remove fallen leaves. Fungicide is necessary in spring as leaves expand. Susceptible varieties must be protected with fungicides before disease is present for good control.


Phomopsis needle and twig – Serious in wet seasons. Needles, twigs and smaller branches turn brown to reddish-brown; gradually die back. Tiny black dots appear later on infected parts. May be confused with normal fall browning, winter injury, spider mites, etc. Prune or remove blighted plants. Spray fungicide.


Cankers are diseased areas of the bark. Many different kinds of fungi and a few bacteria may cause them. The outer bark may appear abnormal. Inner bark is brown and discolored. In time the bark may fall off. Leaves beyond the canker may yellow, scorch or die. Usually canker-causing pathogens can infect only hosts that have been injured or stressed. Trees in decline often lose branches to cankers. Management of canker disease includes avoiding unnecessary injuries and knowing and supplying the maintenance needs of the host to reduce stress. Prune out diseased branches well below the visible infection. After each cut, disinfect pruning tools with rubbing alcohol or 10 percent household chlorine bleach in water. With Rhizoctonia/Phoma canker or die back, stems and leaves may become blackened or blighted. Shoots beyond necrotic area wilt and die. Worst in wet weather. No chemical control. Remove severely affected plants. It may be necessary to increase air circulation by pruning overhanging shrubs and improve drainage by amending soil.

Crown gall

Crown Gall

General and serious. Euonymous extremely susceptible. Small to large, hard, rough galls on roots, crown, or canes. Use certified and disease-free stock. Rounded galls with irregular rough surfaces on roots and lower stems. Avoid nursery stock with galls. Avoid wounding stems or roots. Prune out and destroy affected plant parts. Use disinfectants on cut surfaces. Destroy severely affected plants. Carefully remove and destroy infected plants or plant parts. Avoid wounding. Use strict sanitation measures.

Fire blight

Fire Blight

General and serious. New shoots suddenly appear as if scorched by fire. Leaves cling to twigs. Cankers may be present on twigs and branches. Prune blighted parts in dormant season or in late summer or fall when weather is dry. Dip pruning tools in 70 percent alcohol or 10 percent household bleach between cuts. No chemical control suggested. Cultivars vary in susceptibility.

Leaf and Flower Gall

Leaves become thickened or fleshy galls that then turn pale green or white. The entire blossom may become a fleshy gall covered with a whitish bloom. Usually, chemical control is not warranted. Pick off and destroy galled parts, if feasible. If there is severe infection, you may apply the correct fungicide.

Leaf spot

Leaf Spots

Leaf spots may be caused by a variety of fungal pathogens and a few bacterial ones. Anthracnose causes brown lesions on the leaves, in which tiny fruiting bodies may be seen with a hand lens. Anthracnose is a term used for a group of loosely related fungal diseases that often cause blotches along leaf veins or leaf spots, and can cause twig blights and cankers. Bacterial leaf spot has small, water soaked circular spots that eventually turn brown to purple. Twigs may become girdled, resulting in a blight. Prune and remove affected parts. Apply a fungicide several times beginning when leaves emerge in the spring. Some leaf spots are characterized by large, brown irregular blotches. Others are small, silver gray circular spots or target shaped. Most are uncommon or secondary, following injury to leaf. Few leaf spots seriously damage the host and control can seldom be achieved after the infection is seen. Reasons for considering chemical control on woody ornamentals in subsequent years vary. In some cases, non-chemical management practices should be used. Remove and destroy fallen leaves and twigs. Prune out dead twigs and branches. Avoid the use of high nitrogen fertilizers that can cause new leaves to be very succulent and more disease prone.


Above-ground symptoms depend on the level of infestation. At high levels, there may be stunting, yellowing and an unthrifty appearance. Symptoms may be confused with mineral deficiency, drought, herbicide injury or other soil-borne diseases. Roots have small to large galls and may be excessively branched as well as dark brown to black lesions on roots to overall browning. Roots are usually discolored. Control recommendations depend on species present.

Powdery mildew

Powdery Mildew

Powdery white moldy patches on leaves. Remove badly affected shoots. Prune to thin out branches. Spray with fungicide when mildew appears.

Phytophthora Dieback

Terminal buds and leaves turn brown. Evergreen leaves roll up and droop as though in a winter condition. Cankers are formed on the stems. If stems are girdled, all parts above will wilt and die. Prune and remove affected branches.

Phytophthora rot

Phytophthora Root and Crown Rot

Usually, plants slowly decline in vigor and die. Brownish cortical tissues appear in the root and crown areas. Often associated with wet feet. Maintain good drainage and vigor.

Root Rot

Root Rot can be caused by a wide number of fungi. Few of these can be controlled in the landscape, especially on large trees. With Phytophthora root rot, the leaves wilt. Growth is stunted. Fine roots decay and cankers may develop at the base of the stem. Fungicides are available, but their use generally is not recommended for established plantings. Remove and destroy affected plants. If practical, improve soil drainage and replant with a more tolerant variety.


Serious in wet weather. Dull, olive to black velvety or scurfy spots on leaves. Leaves may yellow and fall off. May also appear on fruit. Varieties vary in susceptibility.

Shoot Blights

Common and severe in wet springs on shaded or crowded plants. Immature leaves turn black and die. Flower buds may be entirely black. Spots and blotches on leaves. Annually prune for good air circulation. Prune out blighted portions. Disinfect tools between cuts. Avoid over fertilization with nitrogenous materials. Control borers.

Ventricillium wilt

Verticillium Wilt

Leaves become pale, wilt, and fall early, starting at base and spreading upward. Stems show brownish green streaks under bark. Branches die back. Dig up and remove affected plants, roots and all. Avoid replanting in same spot for 5-6 years and/or replant with resistant species.

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